Antenna pedestal



April 11, 1967 M. SULITEANU 3,313,502

ANTENNA PEDESTAL Filed May 28, 1965 5 Sheets-Sheet l D U i aa-l INVENTOR.

MEMAHEM SULITEA NU BY flwffuh ATTORNEY April 11, 1967 M. SULITEANU ANTENNA PEDESTAL 3 Sheets-Sheet 2 Filed May 28, 1965 R m m V m MENAHEM SULITEANU ATTORNEY April 11, 1967 M. SULITEANU 3,313,502

ANTENNA PEDESTAL Filed May 28, 1965 6 Sheets-Sheet 5 INVENTOR.

MENAHEM SULITEANU ATTORNEY ANTENNA PEDESTAL Menahem Suiiteanu, Palo Alto, Calif., assignor to Sylvania El ctric Products Inc, a corporation of Delaware Filed May 23, 1965, Ser. No. 459,763 Claims. (Cl. 24845) This invention relates to antennas and more particularly to a three-axis pedestal for airborne, ship or ground-based antennas.

Versatility in movement of antennas is needed to meet the requirements in shipboard, airborne and even groundbased antenna systems because of the increasing variety of objects to be tracked and other operating conditions imposed upon such systems. Pedestals for such antennas must provide this versatility of movement without compromising rigid support needed to maintain and insure positional accuracy of the reflector. Three-axis pedestals in the past have necessitated the use of counterwe-ights and massive structural components to provide rigidity and balance of the moving parts with a consequent increase in weight, size and cost. Moreover, the multiple axis design has often resulted in a configuration in which moments of force developed by wind loading are magnified and thus require additional compensation. Also the problems of servicing and maintaining moving parts of the assembly, such as bearings and drive mechanisms, are more diflicult because of the complexity and size of these components required for precision movement of the massive structure.

An object of this invention is the provision of a threeaxis pedestal in which the axes of rotation are closely spaced to the base bearing for reducing force moments and thus minimizing the eflects of loading time to wind and the like.

Another object is the provision of a three-axis pedestal which may be readily converted to a two-axis pedestal without structural changes or any redesign of the antenna assembly.

Another object is the provision of an antenna pedestal in which the weigh of the antenna is distributed over a large bearing surface so that large antennas (30 feet and 60 feet in diameter or more) may be supported with low unit bearing pressures.

Another object is the provision of a three-axis pedestal in which the three axes intersect each other at a point close to the center of gravity of the reflector.

Another object is the provision of a lightweight pedestal with a semi-circular yoke supported for rotation about a cross axis at the yoke periphery.

Another object is the provision of a pedestal with a semi-circular prestressed yoke for rigidly supporting the antenna.

Another object is the provision of a pedestal With a unique ring-type slide bearing for supporting movement of the entire structure about the azimuth axis.

In accordance with the invention, a vertically extending cradle is supported on an azimuth bearing for rotation about a vertical (azimuth) axis and has an elongated circularly curved bearing area which supports the periphery of a circularly curved yoke for rotary movement in the plane of and relative to the cradle about a cross axis. The spaced upper ends of the yoke have elevation bearings, respectively, which support the antenna for rotation about an elevation axis which intersects the azimuth and cross axes. The yoke is prestressed by its connection to the antenna thereby contributing to the rigidity of the assembly.

The weight of the antenna is uniformly distributed by the yoke over the entire cradle and is so supported in the yoke that the center of gravity of the antenna is sub- 3,3135% Patented Apr. I1, 1967 stantially at the intersection of the azimuth, elevation and cross axes. The azimuth bearing diameter approximates the overall dimension of the yoke providing maximum pedestal stability and minimum load per unit length of the bearing. The cradle and yoke may be locked together to prevent relative movement therebetween and thereby convert the three-axis pedestal into two-axis pedestal with no further structural changes. A simplified slide-type azimuth bearing construction is utilized as a result of the pedestal configuration and the balanced distribution of load.

These and other objects of the invention will become apparent from the following description of a preferred embodiment thereof reference being had to the accompanying drawings in which:

FIGURE 1 is a front view of an antenna pedestal embodying this invention with the antenna only partially shown, the view being a section taken on line 1-1 of FIGURE 4;

FIGURE lA is a greatly enlarged section of the azimuth bearing;

FIGURE 2 is a side elevation partly in section of the pedestal;

FIGURE 3 is an enlarged transverse section taken on line 33 of FIGURE 1; and

FIGURE 4 is a section taken on line 4-4 of FIGURE 1 with the shroud broken away for showing the azimuth drive mechanism.

Referring now to the drawings, the antenna system comprises an antenna it? supported for rotation about axis 11 on yoke 12. A cradle 1 supported on base 15 by bearing 16, see FIGURES 1 and 2, for rotation about a vertical axis 17, called the azimuth axis, supports the yoke 12 on bearings 18 for rotation about a cross-axis (see FIGURE 2). The three axes 11, I7 and 19 intersect at the point C (FIGURE 1) which preferably corresponds to (or nearly so) the center of gravity of the antenna 10.

Antenna it may be any structure for which movement about three axes is desired and typically is a parabolic reflector together with a primary feed element, such as a waveguide horn, at the focal point of the reflector designed to illuminate the reflector surface with electromagnetic wave energy. The details of construction of the antenna ltl do not, per se, constitute part of this invention which may be practiced with any movable structure such as reflectors for optical systems, solar energy systems, and other like systems. An example of a structure typically adaptable for use as antenna It is the rigid foamed-plastic assembly described in Patent No. 3,167,776 of M. Suliteanu.

Antenna it) includes a pair of oppositely and outwardly extending support members 21 and 22 which are secured to or are integral with the body of the antenna and which have journals 23 and 24, respectively, supported in elevation bearings 25 and 26 mounted in the upper ends of yoke 12. The axes of bearings 25 and 26 are coincident with the axis 11 about which the assembly 10 rotates in elevation.

In order to increase the rigidity of the structure, yoke 12 is prestressed by a slight inward pulling on its upper ends by members 21 and 22 of the antenna 10. To this end, journals 23 and 24 have outboard flanges 23a and 24a removably secured thereto which press against the outer surface of the yoke through bearings 27. In eflect, antenna support members 21 and 22 together with the journals comprise a diametralbeam which preloads and stifiens the yoke and antenna assembly.

The elevation drive system comprises two electrically energized motors 28 and 29, see FIGURE 2, mounted on yoke 12 above and adjacent to journal bearing 26, an endless belt or chain 30 which frictionally engages and is driven by drive sheaves 28a and 29a on the respective motor shafts, and a drive ring 31 secured through flange 24a to journal 24 and frictionally engaged by the belt which preferably is fully wrapped around the ring. An idler wheel 32 between the motors is adjustable transversely of the belt to change belt tension. A shroud 33 protectively covers the mechanism.

Motors 28 and 29 drive belt in opposite directions; i.e., motor 28 rotates in a counterclockwise direction as viewed in FIGURE 2 when energized and motor 29 rotates in a clockwise direction when energized. The direction of rotation of the antenna 19 about the elevation axis 11 is therefore determined by selective energization of either of the motors 23 and 2?. This differential drive system as well as the azimuth drive system described below preferably include a unique damping action for compensating mechanical resonance in the drive system and load and is described and claimed in the copending application of M. Suliteanu and F. M. Fonda, Ser. No. 476,555, filed Aug. 2, 1965. Although the elevation drive system presents an unbalanced weight distribution on the yoke, the preloading of the yoke as described above provides suflicient structural stiffness to substantially overcome the effects of this condition.

Yoke 12 comprises an elongated semi-circularly shaped upwardly curved frame 35 having a center plane containing azimuth axis 17 and having housings 36 and 37 at its upper ends for elevation bearings 25 and 26, respectively. Frame 35 comprises a transverse upper portion 39, see FIGURE 3, to the opposite sides of which L-shaped retainers 4i and 41 are secured and thus the yoke frame constitutes an inverted channel member which fits over the upper part of the cradle for guided arcuate movement relative thereto.

Cradle 14 comprises a lower dish-shaped double-shell circular frame 42 and a vertically projecting circularlycurved upper part 43 which is secured to the frame 42 directly and by side braces 44. Upper cradle part 43 is circularly-curved in the direction of its length and has an upper plate 45, see FIGURE 3, and outwardly projecting side flanges 46 and 47. The channel-shaped underside of the yoke overlies the upper cradle part 43 and is supported thereon by a plurality of bearings 18 spaced therealong as shown in FIGURE 1. Each bearing 18 comprises antifriction pads or blocks 49 between the transverse yoke portion 39 and cradle plate 45, side blocks 51 between the sides of flanges 46 and 47 and the respective cradle retainers and 41, and lower bearing blocks 52 between the underside of flanges 46 and 47 and the inwardly extending ends of the retainers. These antifriction pads by way of example may comprise steel blocks with thin reinforced Teflon lining. Yoke 12 is thus constrained in its movement relative to the cradle over these hearings to a circular are which preferably has a center C at the intersection of the three antenna axes.

Disposed within the framework of upper cradle part 43 are tubular conduits 54 and 55 which extend the length of this cradle part under bearing support plate 45. These conduits preferably are supported in lightweight foamed-plastic filler 56 within the cradle framework and provide channels for power cables for the elevation drive motors 28 and 29 and a feed cable for antenna 10. Conduits 54 and 55 intersect vertical cable wells 57 and 58, respectively, which provide openings through the lower cradle frame 42 for external connection of the cables. Elevation drive motor cables 66 and antenna feed cable 62 have smaller diameters than these conduits and thus are adapted to move freely longitudinally within these conduits as the yoke moves relative to the cradle. Antenna feed cable 62 extends through a rotary joint 63 at cradle bearing housing 36 for connection through journal 23 to the feed. device of the antenna. The power and feed cables preferably make slack loops 1 below base 15 to provide suflicient length to accommodate rotation of the yoke in the cradle.

Base 15 has an annular side wall 65 on which azimuth bearing 16 is mounted. Bearing 16 comprises an annular V-shaped ring defined by flat side members 66 and 67, see FIGURE l-A, secured to the upper part of base wall 65 and inclined downwardly and upwardly, respectively, therefrom. Antifriction pads 68 and 69, similar to the pads described above, are mounted on these ring side members and are engaged by an annular split collar 71 which is securely connected to and depends from the periphery of lower cradle frame 42. Collar 71 comprises an upper portion 71a permanently secured to the cradle frame and a lower portion 71b removably secured to the upper collar portion by bolts; the upper and lower portions 71a and 71b of the collar having annular recesses 72 and 73, respectively, within which the .antifriction pads 68 and 6d are seated.

The outer surface 75 of collar 71 constiutes the azimuth drive surface of the assembly adapted to be engaged and rotated by an endless belt 77. This belt is driven by sheaves 78 and 79, see FIGURE 4, rotated by azimuth drive motors St) and 81, respectively, and adjusted for tension by an adjustable intermediate idler wheel 82. Belt 77 frictionally engages the drive surface 75 of collar 71 and is driven in one direction by motor 78 and in the opposite direction by motor 79. Belt 77 engages less than the entire periphery of the collar drive surface 75 and may, for example, engage as little as one quarter of the periphery of the collar without impairing the efficiency of the drive system. A second identical drive system may be mounted on the base diametrically opposite the one described above to balance the drive forces and increase the drive friction. This azimuth drive system is described in detail in the aforementioned copending patent application to M. Suliteanu and F. Fonda. A shroud 83 secured around the base protectively covers the azimuth drive mechanism, the collar 71, hearing 16 and associated parts from foreign matter.

In order to rotate the yoke on and relative to the cradle, belts 84 and 85 are secured to the upper outer ends of the yoke, one of which connections is shown at 86 in FIG- URE 2, and are wound on drums 87 and 88 mounted on the upper cradle 43 for rotation about the respective drum axes. Drums 87 and 33 are driven by motors 89 and 90, respectively, the energization of which is synchronized so that one or the other of belts 84 and 85 is being wound on its drum at one time to displace the yoke in the cradle in the desired direction. During such movement, the belt which is being unwound from its drum is maintained in slight tension to eliminate any play therein and to provide instantaneous response to reversal of direction of rotation of the yoke within the cradle. Rotary movement of the yoke about the cross axis 19 is limited to the extent that the arc length of the yoke is greater than that of the upper cradle part, and such limits are indicated by the broken line outline of the elevation bearing housings in FIGURE 1. Typically, such motion is limited to an arc of :30 degrees from the center position. In order to protect the moving parts and bearings from foreign matter, a bellowtype covering, not shown, may be mounted between the upper parts of the yoke and the cradle over the portion of the yoke that extends about the cradle.

The three-axis antenna pedestal described above may be readily converted to a two-axis pedestal by simply locking yoke 12 to the upper part of the cradle to prevent relative movement between these parts of the cradle. This may be accomplished, for example, by locking drums 87 and 88 to which the yoke actuating belts 84 and 85 are wound so that the drums cannot rotate. Alternative- 1y, these parts may be locked together by rigid plates, detents or similar locking devices. This eliminates motion of the antenna about the cross axis 19 and retains motion about the remaining two axes.

In a preferred embodiment of the invention, the structural members of the assembly are fabricated from rigid plastic foam and fiberglas reinforced surface layers. This type of construction permits fabrication by low-cost molding techniques, has a high degree of immunity to the effects of weather and has inherent dimensional stability due to its low thermal coefficient of expansion. The reduction of wind-induced moments, the balanced distribution of load through the cradle to the base and the lightweight construction combine to reduce the loading on the base, thus minimizing the wear and maintenance of the azimuth bearing and requiring less massive foundations. Furthermore, the unique antifriction slide-type bearing described above not only provides stable accurate support of moving parts of the pedestal but also can be made with a large diameter at reasonable cost so that large diameter drums may be employed for increasing the positioning accuracy of the pedestal.

Modifications, changes and improvements to the above described embodiment of the invention may be made by those skilled in the art without departing from the scope of the invention. The appended claims define the novel feature of the invention.

1 claim:

1. A three-axis pedestal for supporting an antenna for rotation about three axes comprising a base having a slide bearing ring projecting from the side thereof,

a cradle supported on said ring for rotation about a first axis and comprising a lower horizontal frame having a peripheral split collar overlying and supported on said ring for sliding movement thereon, and

an upper cradle part secured to and extending upwardly from said cradle frame and having a vertical central plane containing said first axis,

bearing means supported on said upper cradle part on the arc of a circle having a center on a second axis and in said plane,

a yoke having an elongated channel-shaped frame supported on said bearing means for rotary movement about the second axis relative to the upper cradle P said yoke having spaced bearings at upper opposite ends thereof aligned along a third axis,

said antenna being supportable in the bearing of said yoke for rotation about said third axis, azimuth drive means engageable With the collar of said cradle for rotating the cradle about the first axis, elevation drive means supported on said yoke and engageable with the antenna for rotating same about said third axis, and yoke drive means mounted on the upper part of said cradle and engageable with the yoke for rotating the latter relative to the cradle about said second axis.

2. The pedestal according to claim 1 in which said first, second and third axes intersect each other at a point proximate to the center of gravity of said antenna.

3. The pedestal according to claim 1 in which the yoke drive means comprises a pair of rotatable drums mounted on opposite sides, respectively, of the upper part of said cradle, means for selectively alternately rotating said drums, and belts connected to said drums, respectively, and to said yoke on opposite sides of the second axis whereby said yoke is moved relative to the cradle selectively in opposite directions about the second axis as one or the other of the belts is wound on the associated drum.

4. The pedestal according to claim 1 in which the upper cradle part has an elongated cylindrical upper plate having an axis of formation coincident with said second axis and similarly curved side flanges projecting therefrom, said bearing means on the upper cradle part comprising antifriction slide blocks engaging said plate and the sides and undersides of said flanges whereby movement of the yoke relative to the upper cradle part is constrained to a circular path.

5. The pedestal according to claim 1 in which said upper part of the cradle has conduits coextensive therewith, said lower frame having a central well intersecting said conduits whereby power and feed cables to said elevation drive means and said antenna, respectively, extend therefrom and through said conduits and Well for external connection.

References Cited by the Examiner UNITED STATES PATENTS 2,512,636 6/1950 Flynt 741 CLAUDE A. LE ROY, Primary Examiner.

J. PETO, Examiner. 

1. A THREE-AXIS PEDESTAL FOR SUPPORTING AN ANTENNA FOR ROTATION ABOUT THREE AXES COMPRISING A BASE HAVING A SLIDE BEARING RING PROJECTING FROM THE SIDE THEREOF, A CRADLE SUPPORTED ON SAID RING FOR ROTATION ABOUT A FIRST AXIS AND COMPRISING A LOWER HORIZONTAL FRAME HAVING A PERIPHERAL SPLIT COLLAR OVERLYING AND SUPPORTED ON SAID RING FOR SLIDING MOVEMENT THEREON, AND AN UPPER CRADLE PART SECURED TO AND EXTENDING UPWARDLY FROM SAID CRADLE FRAME AND HAVING A VERTICAL CENTRAL PLANE CONTAINING SAID FIRST AXIS, BEARING MEANS SUPPORTED ON SAID UPPER CRADLE PART ON THE ARC OF A CIRCLE HAVING A CENTER ON A SECOND AXIS AND IN SAID PLANE, 